The present invention relates to novel methods for preparing quinoline-2,3-dicarboxylic acids. These acids are useful intermediates in the preparation of herbicidal pyridine and quinoline imidazolinone herbicidal compounds.
The herbicidal pyridine and quinoline imidazolinone compounds prepared from the present compounds include 2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)quinoline-3-carboxylic acid, esters and salts thereof and are disclosed in European Patent Application No. 0,041,623, incorporated herein by reference. These herbicidal imidazolinyl quinolinecarboxylic acids may be prepared by the procedure described in U.S. Pat. No. 4,518,780 (incorporated herein by reference) by cyclization, under basic conditions, with an appropriately substituted 2-carbamoyl quinoline-3-carboxylic acid, that, in turn, is prepared by the reaction of a substituted quinoline-2,3-dicarboxylic acid anhydride and appropriately substituted aminocarboxamide or aminothiocarboxamide. Quinoline-2,3-dicarboxylic acid anhydrides are readily prepared from the diacids by procedures well known in the art. However, the diacids themselves are not readily available.
Existing procedures for preparing esters of quinoline-2,3-dicarboxylic acid include the Friedlander reaction of 2-aminobenzaldehyde with diethyloxalacetate, as described by L. Hozer and S. von Niementowski, J. Prakt. Chem., 116(2): 43 (1927) and P. Caluwe, Tetranedron, 36: 2359 (1984), and the ozonolysis of acridine as described by A. Godard, G. Zueguiner, P. Pastour in Bull. Soc. Chim. France, 906 (1971). These methods are not suitable for the manufacture of large quantities of materials because of difficulty in preparing and storing 2-aminobenzaldehyde. 2-aminobenzaldehyde is not only unstable, but there are limited supplies of acridine in order to prepare said 2-aminobenzaldehyde. Therefore, other routes have been preferred.
On such other synthesis is disclosed in pending application for U.S. Letters Patent of Robert Doehner, Ser. No. 698,192 filed Feb. 4, 1985 (incorporated herein by reference) which describes a method for the preparation of quinoline-2,3-dicarboxylic acid and esters thereof by reacting a beta-anilino-alpha,beta-unsaturated ester with an immonium salt (commonly called a Vilsmeir reagent). The beta-anilino-alpha,beta-unsaturated esters are obtained by the reaction of appropriately substituted anilines with ketoesters or dialkyl acetylene dicarboxylates.
Unfortunately, the availability of ketoesters and dialkyl acetylene dicarboxylates, such as diethyloxalacetate and diethyl acetylenedicarboxylate is limited, thereby restricting the quantities of anilinofumarate, a precursor to quinoline-2,3-dicarboxylic acid.
Co-pending applications for U.S. Letters Patent of D. Maulding, Ser. No. 902,275 and 902,274, filed concurrently herewith and incorporated herein by reference, provide effective methods for the preparation of anilinofumarate by reacting dichlorosuccinates with specified amines.